class Scratch {
    constructor(page, opts) {
        opts = opts || {}
        this.page = page
        this.canvasId = opts.canvasId || 'canvas'
        this.width = opts.width || 340
        this.height = opts.height || 150
        this.maskColor = opts.maskColor || '#D2D2D2'
        this.size = opts.size || 10
        this.r = this.size * 2
        this.area = this.r * this.r
        this.scale = opts.scale || 0.3
        this.totalArea = this.width * this.height

        this.init()
    }

    init() {
        this.show = false
        this.clearPoints = []
        this.ctx = uni.createCanvasContext(this.canvasId)
        this.drawMask()
        this.bindTouch()
    }

    drawMask() {
        this.ctx.setFillStyle(this.maskColor)
        this.ctx.fillRect(0, 0, this.width, this.height)
        this.ctx.draw()
    }

    bindTouch() {
        this.page.touchStart = (e) => {
            this.eraser(e, true)
        }
        this.page.touchMove = (e) => {
            this.eraser(e, false)
        }
        this.page.touchEnd = (e) => {
            if (this.show) {
                this.ctx.clearRect(0, 0, this.width, this.height)
                this.ctx.draw()
            }
        }
    }

    eraser(e, bool) {
        const len = this.clearPoints.length
        let count = 0
        const x = e.touches[0].x;
        const y = e.touches[0].y
        const x1 = x - this.size
        const y1 = y - this.size
        if (bool) {
            this.clearPoints.push({
                x1: x1,
                y1: y1,
                x2: x1 + this.r,
                y2: y1 + this.r
            })
        }
        for (const item of this.clearPoints) {
            if (item.x1 > x || item.y1 > y || item.x2 < x || item.y2 < y) {
                count++
            } else {
                break
            }
        }
        if (len === count) {
            this.clearPoints.push({
                x1: x1,
                y1: y1,
                x2: x1 + this.r,
                y2: y1 + this.r
            })
        }
        if (len && this.r * this.r * len > this.scale * this.totalArea) {
            this.show = true
        }
        this.clearArcFun(x, y, this.r, this.ctx)
        this.ctx.draw(true)
    }

    clearArcFun(x, y, r, ctx) {
        let stepClear = 1
        clearArc(x, y, r)

        function clearArc(x, y, radius) {
            const calcWidth = radius - stepClear
            const calcHeight = Math.sqrt(radius * radius - calcWidth * calcWidth)

            const posX = x - calcWidth
            const posY = y - calcHeight

            const widthX = 2 * calcWidth
            const heightY = 2 * calcHeight

            if (stepClear <= radius) {
                ctx.clearRect(posX, posY, widthX, heightY)
                stepClear += 1
                clearArc(x, y, radius)
            }
        }
    }
}

export default Scratch